1. Field of the Invention
The present invention relates to a positioning device for a positioning element, which is rotationally displaceable with respect to a first axis, and which includes a positioning member which engages with the positioning element, the positioning member being rotatable about a second axis that is perpendicular to and spaced from the first axis.
2. Description of the Related Art
Positioning devices of this type are provided in signature feeders with the model designation P311, which are components of saddle stitchers marketed by Heidelberg Web Systems Inc., Durham, USA under the name Pacesetter 1000. These positioning devices include a sprocket provided on the positioning element with which a worm gear meshes. The positioning element is provided with a valve including a control disc having a hole pattern, which, under normal operating conditions, periodically produces a fluid connection between a suction device and a vacuum generator. The suction device functions in the signature feeder to open the signatures which are then transferred along a saddle chain of the saddle stitcher. The suction device includes suction boxes which are in fluid connection with the vacuum generator during a periodically recurring time window and applies suction to a respective arm of a respective signature feeder within this time window.
Opener drums are disposed parallel to the axis of the suction device, and each of the suction boxes for a respective one of the signature arms is disposed thereon. For dispensing the signatures to the saddle chain, the suction boxes are aerated after the time window has expired such that the signatures separate from the suction boxes. The timing of the separation of the signatures from the suction boxes must be adaptable to the processing speed and to the material properties of the signatures. Accordingly, the control disc is rotationally displaceable.
A transfer drum precedes the gripper drum. The transfer drum transfers signatures taken from a signature stack using the separating device and releases the signatures to the opener drum.
The signature feeders include an operating side on which operating elements are disposed. The operating elements include a rotary knob for turning the worm gear which, via turning of the sprocket meshing therewith, rotationally displaces the control disc, and thus, the time window and the timing at which the signatures separate from the suction boxes is changed.
In some instances, the required displacement of the control disc requires that the worm gear must execute a plurality of revolutions. This makes it more difficult to a reproducibly set the timing at which the signatures separate from the suction boxes.